This invention relates to electrophotographic copiers and duplicators, and more particularly to the optical imaging apparatus in such copiers or duplicators.
Electrophotographic copying and duplicating equipment, such as optical copiers and duplicators, which can produce fused toner copies of an original image on suitable copy sheets, are well known. See, for example, U.S. Pat. Nos. 4,139,297 and 4,390,267. Typically, such equipment includes optical imaging apparatus consisting of a transparent platen for holding an original document to be copied, flash lamps for illuminating the document, a lens system, and light control devices for focusing imaging rays, which are reflected from the background portions of the original document, onto an image frame area of a charged photoconductive image-bearing member.
With such imaging apparatus, a single latent image of the original document can conventionally be formed on an image frame area of the charged photoconductor. The reflected light rays, upon impinging on portions of the charged (photoconductive) image frame, expose such portions, thereby dissipating charges therein. Undissipated portions of the image frame area, that is, those portions where latent charges remain, correspond to the image portions of the original document--hence constituting the latent charge image of such original.
Various size documents, for example, 17".times.11" original documents and 8.5".times.11" original documents can be optically imaged in this manner. As is well known, the latent electrostatic image thus formed can thereafter be processed through sequential steps of the copier or duplicator, in which the image is developed, transferred to a suitable receiver sheet, and then fused onto such receiver sheet in order to form a sheet copy of the original document.
Conventionally, optical copiers and duplicators, which for example have a closed loop sixty-six (66") inch, six (6) image frame area, seventeen (17") inch wide photoconductor, can sequentially function as above to produce both 17".times.11" and 8.5".times.11" copies. Typically, such copiers and duplicators do so in what can be characterized as a single imaging mode. Such a copier or duplicator operates in a single imaging mode when it forms and processes only a single image, in a single image area of its photoconductor, during each of its sequential steps of image formation, development, transfer, and fusing. Additionally, each such copier or duplicator forms the 17".times.11" and 8.5".times.11" images on its photoconductor such that the long dimension of each image, that is the 17" and the 11" dimensions respectively, are across the 17" width of the photoconductor. As such, the maximum number of full 17".times.11" images that can be formed in one complete revolution of the photoconductor is six (6), while the similar number for full 8.5".times.11" images is only seven (7)--that is, 66".times.8.5".
It is clear that in such copiers and duplicators, the productivity or number of 8.5".times.11" images, relative to 17".times.11" images, is undesirably limited. Furthermore, much of the in photoconductor such a copier or duplicator is unused during the production of such 8.5".times.11" images.